The present invention relates to specimen or sample inspection systems and more particularly to systems in which human operators inspect a substantial number of individual specimens to locate a particular subset such as "suspicious" or irregular specimens. As used herein, the term "specimen" is not necessarily limited to a medical or biological specimen but may more generally extend to any sample item or portion of a group as a whole.
The present invention may find particular use in a variety of contexts such as, for example, examining exfoliated tissue samples in a cervical Pap smear test, examining silicon wafers in an integrated circuit manufacturing process, and other materials inspection processes. In a typical scenario, a human inspector must inspect and analyze a substantial number of specimens each day to determine whether the specimens divert from some predetermined norm. Abnormal specimens are identified and are subject to further, more detailed review. The subsequent, more detailed review may require a reviewer with additional expertise, such as a pathologist in the case of the Pap test. In a usual case, most of the specimens are considered "normal," or "within normal limits," and therefore need not be rejected or subject to additional scrutiny. Depending on the detail and scope of this inspection and analysis, this additional scrutiny can unfortunately be a very slow, painstaking and costly process.
For purposes of illustration, the present invention will be described in the context of cytological specimen analysis, such as cervical Pap smear analysis. Pap smears, which are routinely taken from women, facilitate the detection of pre-cancerous changes and/or the early stages of cancer, thus reducing the chances of any cancer or related abnormal condition from spreading or advancing with the resultant negative impact on the prognosis for the patient. A Pap smear is prepared by first collecting a vaginal, cervical and endocervical tissue sample from a patient. The sample is then fixed to a slide, for instance by alcohol fixation, and Pap-stained to enable microscopic analysis. Alternatively, rather than preparing a Pap smear, the specimen may take the form of a liquid-based or monolayer preparation, using instruments manufactured, for instance, by AutoCyte or Cytyc. In practice, the slide is then screened by a highly skilled technician ("cytotechnologist"), in an effort to identify possible cellular abnormalities in the specimen and to determine the specimen adequacy. The cytotechnologist generates notes regarding each specimen deemed to have possible abnormalities. The cytotechnologist then provides the specimen slide, together with notes of his or her findings, to an expert pathologist (i.e., specialized physician) for further review and final specimen diagnosis.
To screen a Pap smear specimen, the cytotechnologist generally views the Pap smear slide containing the Pap smear through a microscope to detect the presence of cancer cells or cells exhibiting other abnormal conditions. Because a cancerous cell may appear in only one of thousands of locations in an otherwise normal-appearing specimen, however, the cytotechnologist must generally examine every area of the slide in order to make a valid (i.e., accurate) determination. Further, many portions of the specimen slide may contain no cells at all, but the cytotechnologist must examine even those areas to at least determine the absence of pertinent (i.e., diagnostically significant) material. Of course, this process of thoroughly screening a specimen for the presence of cancerous or abnormal cells is often laborious, error-prone and costly. Still, cytotechnologists have been known to examine more than 20,000 slides annually in an effort to classify specimens as within normal limits and to identify abnormalities and enable pathologists to diagnose Pap smear specimens. In many cases, this specimen review rate is driven in part by financial concerns such as competition based on the number of specimens analyzed.
Based on the cytotechnologist's primary review (i.e., screening) of the specimen, the cytotechnologist determines either that the specimen contains suspicious material such as pre-cancerous or cancer cells, or that the specimen is apparently within normal limits. Typically, statistically speaking, "suspicious" and "abnormal" specimens may account for approximately 5% to 10% of Pap smears in the United States, in laboratories that are screening asymptomate women. The remaining statistical 95% to 90% of the cases in turn are classified as apparently normal.
If a specimen contains even a single well preserved and well-stained cancer cell out of tens or hundreds of thousands of cells, the cytotechnologist should find the specimen to be suspicious, or atypical or abnormal. Failure to properly identify a specimen as abnormal during this screening process may be disastrous, as it may leave a cancer patient undetected and untreated and may ultimately lead to the death of the patient.
The cytotechnologist forwards all "suspicious," or "atypical" or "abnormal," specimens to a pathologist for detailed review and final diagnosis and "sign-out" in light of the cytotechnologist's notes and findings. One of the pathologist's goals is to analyze the specimen at issue and determine based on medical expertise whether the specimen contains cancerous or pre-cancerous cells. In doing so, the pathologist must strive to minimize both false negative diagnoses and false positive diagnoses, as false negative diagnoses could leave cancer undetected, while false positive diagnoses could result in unnecessary or inappropriate, harmful and costly cancer treatment such as chemotherapy or the like.
Most of the specimens that the cytotechnologist deems to be "apparently normal" are classified as within normal limits, and the analysis of those specimens is completed. However, to minimize the possibility of false negatives in the screening process and to identify cytoteclmologists that may have screening quality performance problems, at least some of those specimens should be subject to a secondary screening, or "re-screening," by a cytotechnologist. In the United States, at least 10% of these "apparently normal" specimens must be randomly selected and re-screened for quality assurance by a different cytotechnologist.
In addition, to further minimize false negatives during the Pap smear screening process, cytotechnologists must spend sufficient time screening each specimen slide. For this reason, legal regulations in some states in America restrict individual cytotechnologists to screening no more than 100 Pap smear slides in a single day. Other states provide even stricter limitations, such as a maximum of 80 slides per day. Assuming an average 7 hour work day, these regulations would have a typical cytotechnologist screening and classifying an average Pap smear slide in no more than 4.20 to 5.25 minutes.
Notwithstanding these maximum limitations, the average number of Pap smear slides screened per day by cytotechnologists in the United States is on the order of only 50 to 60, corresponding to cytotechnologists typically spending less than 7 to 8 minutes reviewing each slide in order to carefully determine whether any abnormal cells are present. Of course, as cytotechnologists spend more time screening each slide, they will theoretically make fewer false negative errors. At the same time, however, as cytotechnologists spend more time screening each slide, they will screen fewer slides each day, and the labor and cost of specimen screening will consequently rise.
A need therefore exists for a more efficient specimen screening system that minimizes the presence of false negative specimen classification errors while reducing the time required to analyze specimens accurately and to compile useful information about suspicious, atypical, or abnormal specimens for reference by diagnostic experts.